In addition to the internal combustion engine, hybrid vehicles standardly have an electric motor that is operated either in a motor operating mode or in a generator operating mode, as a function of the driving situation. In motor operation, the electric motor produces an additional drive torque that supports the internal combustion engine, e.g. during an acceleration phase. In the generator operating mode, the kinetic energy that is released during deceleration of the vehicle is converted into electrical energy (recuperation). The electrical energy obtained in this manner is stored in an energy storage device, such as a battery or a super capacitor, and can be used in other driving situations, for example to propel the vehicle or to supply electrical consumers with energy. In this manner, the efficiency of the vehicle can be significantly improved.
Certain conventional pulse-width modulation rectifiers (PWR) standardly contain a power electronics stage as well as a computing core that is integrated into the PWR. The PWR is controlled by an external control device that calculates a target operating point for the internal combustion engine and for the electric motor as a function of the driver's wishes (acceleration or braking). The pulse-width rectifier is connected to the control device and receives the corresponding operating data or control commands from this device.
FIG. 1 shows a section of an electrical system of a hybrid vehicle. The system includes an electric machine 1 having a pulse-width rectifier 2 that is capable of operating electric machine 1 in motor operating mode or in generator operating mode. In motor operating mode, electric machine 1 supports the internal combustion engine; in generator operating mode, electrical energy is produced that is stored in an energy storage unit, here a battery 3.
Electric machine 1 and battery 3 are connected to one another via pulse-width rectifier (PWR) 2. PWR 2 determines the power level and operating mode of electric machine 1 and is correspondingly controlled by a control device 6.
Pulse-width rectifier 2 contains its own power electronics system, as well as a computing device, and is connected to external control device 6 via a CAN bus 4. Control device 6 determines the driver's wishes (e.g. braking or acceleration) and communicates corresponding items of information or control commands to pulse-width rectifier 2. Here, in particular the state of charge (SOC) of energy storage device 3 is also taken into account so that this device will not be overcharged during generator operation.
Pulse-width rectifier 2 and control device 6 are connected to terminals 15, and are standardly switched on through actuation of the ignition lock (KL15).
Certain conventional pulse-width rectifiers 2 are constructed such that when there is a disturbance in the communication connection (CAN bus 4) they switch to a safe state in which electrical energy is no longer produced. This prevents pulse-width rectifier 2 from overcharging energy storage device 3 during generator operation. However, in this safe state no electrical energy is produced at all, so that energy storage device 3 will become discharged relatively quickly given a large number of connected consumers. In this manner, the vehicle can “die” after a relatively short time.